Inhomogeneous turn-off processes may lead to a local elevation (splitting) of the current density within a semiconductor component. If the current density exceeds a specific threshold value, the semiconductor component is destroyed. Excessive increases in current density may also be based on other causes, for example on a local elevation of the concentration of free charge carriers, which may be caused e.g. by cosmic radiation.
The object on which the invention is based is to specify a semiconductor component in which, even in the case of inhomogeneous turn-off processes or on account of other events, a local excessive increase in the current density within the semiconductor component can be counteracted and destruction of the semiconductor component can thus be prevented.
This object is achieved by a semiconductor component in accordance with embodiments of the invention.
The semiconductor component according to embodiments of the invention has a first and a second contact-making region, and a semiconductor volume arranged between the first and the second contact-making region. Within the semiconductor volume, it is possible to generate a current flow that runs from the first contact-making region to the second contact-making region, or vice versa. The semiconductor volume and/or the contact-making regions are configured according to the invention in such a way that the local flow cross-section of a locally elevated current flow, which is caused by current splitting, is enlarged at least in partial regions of the semiconductor volume.
According to the above described embodiments of the invention, then, the flow cross-section of the elevated current flow, upon occurrence of splitting, is widened, preventively, in order that only small excessive increases in the current density can occur in the case of an inhomogeneous turn-off process, by way of example, within a specific region of the semiconductor volume (on account of the enlarged flow cross-section of the current flow, within a certain region of the semiconductor volume, only a reduced proportion of charge carriers that form the current flow is available for a “potential” local excessive increase in the current density).
The flow cross-section of the current flow is enlarged according to embodiments of the invention by virtue of the fact that the current flow is impeded in the main current flow direction, and/or the current flow is promoted in a direction that is different from the main current flow direction. The direction in which the current flow is promoted is preferably a direction that runs perpendicularly to the main current flow direction. Depending on the application, however, any other direction that does not correspond to the main current flow direction is also taken into consideration.
By way of example, doped zones may be formed in the semiconductor volume in such a way that the ratio of the conductivity in one or more directions that are different from the main current flow direction to the conductivity of the main current flow direction is increased. For this purpose, the doped zones may have conventional doping profiles or retrograde profiles/depletion profiles. The semiconductor component may have, by way of example, a vertical or lateral construction or a combination of the two. In a vertical semiconductor component, the semiconductor volume and/or the contact-making regions are configured in such a way that the current flow, upon occurrence of splitting, is impeded at least locally in the vertical direction (main current flow direction) and/or is promoted in at least one lateral direction. Analogously, in the case of a lateral semiconductor component, the semiconductor volume and/or the contact-making regions are configured in such a way that the current flow, upon occurrence of splitting, is impeded at least locally in at least one first lateral direction (main current flow direction) and/or is promoted in the vertical direction or in a second lateral direction.
In order, for example, to promote the current flow in a direction perpendicular to the main current flow direction, doped zones may be provided in the semiconductor volume, in which case, given e.g. a vertical main current flow direction, the ratio of lateral to vertical conductivity of the doped zones (i.e. the ratio of the conductivity in one or more planes perpendicular to the main current flow direction to the conductivity in the main current flow direction) is designed to be as high as possible. The doped zones have the effect that charge carriers are transported into “remote” regions of the semiconductor volume into which, under “normal circumstances”, i.e. without the doped zones, they would not pass or would pass only in a low concentration. The dimensions of the doped zones are thus established in such a way that the latter extend into, adjoin and/or extend as closely as possible to all regions of the semiconductor volume that are intended to be included by the current flow.
The doped zones are situated for example in emitter zones, base zones or field stop zones of the semiconductor component, but may, in principle be introduced at an arbitrary position within the semiconductor volume. Preferably, the doped zones are provided in and/or near the regions of the semiconductor volume in which the highest field strengths occur. These are the emitter zones, by way of example, in the case of diodes. If the doped zones are provided in the emitter zones, these should advantageously not be provided at the edge of the emitter zones, but rather be buried within the emitter zones (in other words not at or closely below the surface of the emitter zones). This makes it possible to achieve an improved expansion of the local flow cross-section upon occurrence of splitting.
In order to promote the current flow in a specific direction, it is also possible, as an alternative to the provision of a doped zone, for the contact resistance between the semiconductor volume and the first or second contact region to be elevated in such a way that, on the one hand, proper operation of the semiconductor component is ensured and, on the other hand, the flow cross-section of the current flow that enters into the contact-making regions/emerges from the contact-making regions is expanded at the junction between semiconductor volume and contact regions. The contact-making resistance may in this case be brought about both by the choice of a specific metallization material and by a reduction of the dopant concentration in that part of the semiconductor volume which adjoins the contact-making region.
If the contact-making resistance between the semiconductor volume and the contact-making regions is very high, at the junction between the first and/or second contact-making region and the semiconductor volume, low-impedance channels should be formed in the semiconductor volume, which channels are distributed as homogeneously as possible over the junction. Such a provision of low-impedance channels may also be used beneficially in the case of a low contact-making resistance.
A further possibility for expanding the local flow cross-section in the boundary region between contact-making regions and semiconductor volume consists in the contact-making regions not being applied over the whole area, but rather to corresponding surfaces of the semiconductor volume in a patterned manner in the form of individual contact-making zones. In this case, the contact-making zones should be distributed as homogeneously as possible over the surface of the semiconductor volume.
The principle according to the invention may be used in arbitrary semiconductor components, for example in diodes, thyristors, IGBTs, etc.